Apparatus for plating the interior of hollow objects



May 21, 1957 P. PAWLYK 2,792,806

APPARATUS FOR PLATING THE INTERIOR OF HOLLOW OBJECTS Original Filed Oct.8, 1951 5 Sheets-Sheet l agi l l0 v l INVENTOR. t Y PETER PAwLYn BY C\'JM i /oablnum/ ATToRNEYs P. PAWLYK May 21, 1957 APPARATUS FOR PLATNG THEINTERIOR OF' HOLLOW OJECTS 3 Sheets-Sheet 2 Original Filed Oct. 8, 1951INVENTOR. PETER PAWLYK al "Wl",

ATToRNEYs May 21, 1957 P. PAWLYK 2,792,806

APPARATUS FOR PLATING THE INTERIOR OF HOLLOW OBJECTS Original Filed Oct.8, 1951 3 Sheets-Sheet 3 INVENTOR.

PETER PAwLYK [-1578 'A BY mm@ ATTORNEYS United States Patent O APPARATUSFOR PLATING THE NTERIOR OF HOLLOW OBJECTS Peter Pawlyk, Dayton, Ohio,assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio,a corporation of Ohio 2 Claims. (Cl. 118-43) This invention relates toapparatus and methods for the coating of metallic bases with metalliccoats deposited from the vapor state by the thermal decomposition ofmetal-bearing gases. More particularly the invention relates to theuniform coating of the interior of hollow objects of tubular structuresuch as gun barrels and cylindrical bearing surfaces.

This application is a division of my application Serial No. 250,306, ledOctober 8, 1951, now U. S. Patent No. 2,729,190.

A primary object of the present invention is to'provide improvedapparatus whereby the interior plating of hollow objects may beuniformly achieved. i

An important object of the present invention is to provide equipment forthe plating of hollow objects on a mass production basis.

A principal object of the invention is to provide an improved apparatusfor the interior plating of hollow objects.

The invention comprises a gas plating system in which the object to beplated itself forms walls of the plating chamber, and which object isrotated about a slotted tube adapted to bear the volatilizedmetal-bearing compound to the object. Features of the system includemeans for the mounting of the hollow object about the slotted tube forthe rotation of the object, means to direct the ow of the plating gasesuniformly to the interiorrwalls of the object, and means to provide forthe uniformity of plating gas ow through the system.

The invention also includes the feature of ready interchangeability ofplating objects which facilitates the use of mass production methods inthe gas plating of hollow objects. Substantially all materials whichdecompose under the inuence of heat are operable in thej process ofinvention, the compounds containing chomium and nickel, e. g. nickelcarbonyl being most suitable.

The invention will be more fully understood by reference to thefollowing detailed description and accompanying drawings wherein;

Figure 1 is a schematic representation of one embodiment of theapparatus of invention;

Figure 2 is an enlarged sectional view of the object to be platedincluding means illustrating the mounting thereof;

Figure 3 is a View of the left hand end of the structure shown in Figure2;

Figure 4 is a view in section of a modification of the slotted tube ofFigure 2;

Figure 5 is an end view of the structure of Figure 4;

Figure 6 illustrates a modified form of the invention particularlyadapted for the plating of long hollow objects;

Figure 7 is a view of a portion of the structure of Figure 6; and

Figure 8 illustrates a method of mounting a hollow object to secureplating of the entire interior surface.

Referring to Figure '1 the apparatus is shown to comprise the followinggeneral components: a source A of inert carrier gas; a substantiallyconstant temperature source B of metal-bearing gas; a'plating chambersystemv ice C; a recovery system D; and a vacuum pump system E forcontrolling plating gas ow.

Source A may comprise a conventional cylinder 1 containing carbondioxide 2 under pressure. The cylinder is provided with a valve 3 forthe control of gaseous carbon dioxide flow therefrom and a gauge 4 forindicating the flow rate.

The source B of metal-bearing gas: includes a shell 5 containing a solidpowdered metal-bearing compound, chromium carbonyl 6. The shell 5 issurrounded by a hollow coil 7, and the coil and shell are submerged inoil 8 of tank 9, the whole assembly being adapted to be heated byelectric heater 10 to a substantially constant temperature at whichchormium carbonyl has a relatively high vapor pressure. To assure ofadequate temperature control the oil 8 contacts one element 11 of athermostatic control which is suitably connected with heater 10 in theknown manner for regulation of heat input to the system. To avoidlocalized heating a stirrer 12 driven by motor 13 may be employed.

The coil 7 surrounding shell 5 is connected at one end through hollowtube 14 to the valve 3 and the other end thereof is secured in anopening in the lower portion of shell 5. The upper portion of shell 5 isprovided with a second opening in which hollow insulated tubing 15 issecured.

Where coil 1S is of the same material as apertured tube 16 of platingchamber C, now to be described, the members 15 and 16 may be integral.

Plating chamber system C, as mors clearly shown in Figure 2, comprises ahollow, apertured tube 16 of a ceramic material and has the opposingends thereof on the outer circumference secured in gas tight relation tocylindrical metallic bearing members .17 and 18. Members 17 and 1S eachextend along a sufficient length of the circumference of tube 16 toprovide adequate support therefor.

Surrounding the gas carrying apertured tube 16 is a hollow object 19 inthe form of an open ended hollow cylinder and which is to be plated onthe interior wall 20. Cylinder 19 is provided on the outer circumferencewith a layer of heat insulating material, as asbestos, 21, on whichthere is superimposed a resistance heating coil 22 connected toelectrical inlet and outlet 23 and 24, respectively.

The left hand end of cylinder 19 is provided with a ring gasket 25 whichis secured in position by a novel ange 4member 26 recessed as at 27 forengaging the gasket and cylinder along area 28 (Figure 3). Flange 26 isprovided with a central bore 29 into which extends a bearing 30 forrotating engagement with the cylindrical member 17 when the same ispassed through bore 29. As the rate of rotation for member 19 willalways be relatively slow a satisfactory gas seal between thecylindrical shaped members 17 and 30 is established by providing aneoprene gasket 31 about the member 17 in tight fitting relation withthe lateral outward portion of member 26.

The outer circumference 32 of member 26, as at 32, is provided with asurface of friction material, as for example, rubber bonded securely tothe metal of the flange member, and this surface is engaged by a secondfriction member 33 driven through suitable reduction gearing 34 by amotor 35. i

Flange 36 at the right end of cylinder 19 is constructed similarly toiiange 26, and accordingly will not be described in detail. Howeverflange 36 is not driven directly but is rotated with flange 26 andcylinder 19 by means of motor 35. This flange 36 also diers from ange 26in that it is provided with a cylindrical member 39 having an internalbearing surface 40, the purpose of which will be described hereinafter;also flange 36 has openings as at 37 and 38 which serve as exhaust`ports lforthe flow of=waste gases to recovery systemDfthrough pipeline41 having the inlet end engaging bearing surface 4t) and the other endofwhich terminates in a trap 42 for the condensation of metal-bearingvapors. Line 41 may be force fitted into the system and a `featurethereof is the ready removability for mass production purposes. The line41 contains a baflie 68 for directing the flow of gases to a trap 42which is surrounded by cooling water 43 contained .invessel44 havinginlet 46 and outlet 45 forV the passage of the water.

The outlet end of trap 42-is secured tofa vacuum pump 47. Pump 47 is notan essentiall requirement of the system where high flow-rates maybe'obtained by pressure means inthe earlierparts of theapparatus but isessential where it is desirable to maintain low'pressures in theplating-chamber.

Intheoperation of the apparatus of'pF-igures' 1,' `2y and 3 thefobjectto be plated,=after the customary cleaning of the interior surface withacid and alcohol or any con venient-means, is first wound on the outerrside with the layer21 of asbestos. --Thefheating coil Vis then slippedover the Yinsulating material and the gasket ZS-tted over theobjeet end.This assembly is then pressured onto flange 26overthe'ceramic tubelo'each of 'which componentsare initially'secured to the apparatusextending to the left of Figure l.- Flange 36 and gasket 25 are thenpressured onto the right hand end of object 19-and the `removableexhaust 'linesection 41 -is fitted intothe bearing surface 40 of hollowcylindrical member 39 to connect the same with the permanentlypositioned apparatus extending to theright of yFigure l. `This system isthen swept clear of air by flushing as with carbondioxide or other inertgas.

Y buretor 5.

l The solid chromium carbonyl having been heated to vapproximately thetemperature of the oil has thereby attained a relatively large vaporpressure, but without the Vapplication of external pressure to thevapors very little flow thereof takes place. The heated carbon dioxidegas driven by the pressure from cylinder 2 and expanding under theinfluence of the heat absorbed from oil 8 will sweep the carbonyl vaporswith it to line 15 thus re- -ducing or tending to reduce the carbonylvvapor pressure yin the chamber, allowing more carbonyl to vaporize. Alsosincefthe carbon dioxide carrier gas is at substantially theY samepressure as the carburetor, substantially vno cooling of thechromium'carbonyl will be effected by contactl with the carrier gas.

The gases'passingthrough insulated tubing 15' enter the 'chamber definedby hollow object i9 through the kvslots in the ceramic'tube 16. Themotor 35 which as noted is adapted to drive object i9 in rotation hasmeanwhile'been started, and the entering carrier gases will be-givenaslight'circular motion as they approach the Wall 20. 4Theresistanceheater V21?; having been brought up to atemperaturer of about650 F. prior to entry of the plating gas has heated the wall 20 andAupon contact of thegases with the wallthe gases decompose depositingchromium thereon.

The uniformity ofthe chromium deposit isvfimproved by rotation of theobject i9 since the gases are more uniformly distributed within theobject.

The wastegases from the thermal decomposition-are drawn under theinfluence of pump 47 which was acti- I- vated .just prior to .startinggas ow, to the pipe 41 and are -passed to,A trap 42 wherein Ianychromium carbonyl,

- remaining undecomposed, is deposited, through the effect of coolingwater 43 circulating about trap 42.

The waste gases of decomposition such as carbon monoxide then pass on tothe pump and the atmosphere.

The object i9, if assumed to be approximately l in internal diameter,may be thus coated with a .001 of chromium in about l5minutes;when'utilizing a carbon dioxide ow rate at valve 3 of one literper minut-e and an oil bath temperature of 240 F.,. the pressure withinthe object or plating chamber being maintained at about l2 pounds persquare inch absolute.

Various modifications of portions of the structure of Figure l,particularly relating tothe structure of plating vflange 26) whichthensupports the tube 52.

- chamber system C, are setforth in Figures 4 to 9, in-

clusive. Thus in Figures 4 and 5 there is shown a 'slotted tube 48provided with fins 49 .extending therefrom adjacent slots or openings5G, other lins S1 being provided between the slots. The fins 49 servetodirect the ow of gases from the openings 50, while the fins 51 whenused serve to prevent the formation of gaspockets at low gas flow rates.It will be apparent that fins' 49 and Si may be used together orindividually as desired.

Figures 6 and 7 illustrate a modification of the slotted tube of Figurel which is particularly suitable in applica tions where the object to beplated is relatively long. Since the gas carrying tube of ceramicor'other material must be substantially co-extensive with the object inorder to provide for uniform deposition of metal the Weight of theceramic tube may cause a buckling along the length, resulting in shortlife of the equipment. The device of Figures 6 and 7 eliminates thisdifficulty by providing the slotted tube 52 with bearing surfaces 53which Contact in sliding engagement the bearing surface 54 of a -member55 in the form of a U having the arm carrying the surface 54 moreshortened. The longer arm 56 is slotted as at 57 and secured to a flange58 (similar to lt is desirable that slots 57 be spaced closely adjacentthe slots of the gas carrying member to prevent the formation of deadspots in the plating chamber. This support structure may of course alsobe provided on a flangesimilar to 36 of Figure l or supports may, whererequired, be extended from both flanges.

1 lIt will be noted that in Figure l the ends of the object 19 arecovered to a slight extent by the gaskets and flanges, thuspreventingdeposition of metal to the very end of the structure. The apparatus ofFigure 8 overcomes this ob- .jection by providing cylindrical elements59 and tlwhich are secured over the object 6l at opposing ends. Attach-'1 ment of gaskets 62 and 63 and flanges 64 and 65 is 60 must be heatconductive in order to insure that the wall portions of object 6lopposite the elements are com- Vbore openings in said members, said tubebeing open at one end and closed at the other and having apertures inthe .body thereof, each ofsaid members having an annular groove on theinner facethereof, said annular grooves v vreceiving and hermeticallysealing the ends of said hollow open-ended. object, bearings arranged inthe bore openings of said` flange members for supporting said flangemember-andhollow object for rotation, and means for rotating vsaidflange members and hollow object as a unit about said stationary tubeand while supported on said bearings.

2. In combination with a hollow open-ended object to be treatedinteriorly while rotated, means consisting of circular ange members forclosing the open ends of said object, said flange members having acentral bore opening therein, a stationary tube extending through thecentral bore openings in 'said members, said tube being open at one endand closed at the other and having apertures in the body thereof, eachof said members having an annular groove on the inner face thereof, saidannular grooves receiving and hermetically sealing the ends of saidhollow openended object, bearings arranged in the bore openings of saidange members for supporting said flange member and hollow object forrotation, and means for rotating said flange members and hollow objectas a unit about said stationary tube and while supported on said bear-References Cited in the file of this patent UNITED STATES PATENTS1,422,550 Egerton July 11, 1922 2,336,946 Marden et a1 Dec. 14, 19432,449,655 Keiter Sept. 21, 1948 2,503,863 Bart Apr. 11, 1950 2,602,033Lander July 1, 1952 2,685,124 Toulmin Aug. 3, 1954 2,700,365 Pawlyk Jan.25, 1955

